1. Field of the Invention
The present invention relates to a gas-barrier laminate film having excellent gas-barrier capability. More precisely, the invention relates to a gas-barrier laminate film favorably usable in various image display devices, in particular, to a gas-barrier laminate film useful as a substrate for flexible organic electroluminescent devices (hereinafter referred to as “organic EL devices”) and to a method for producing it, and also to an organic EL device.
2. Description of the Related Art
Heretofore, a gas-barrier laminate film fabricated by forming a thin metal oxide film of aluminium oxide, magnesium oxide or silicon oxide on the surface of a plastic substrate or a film is widely used for wrapping or packaging articles that require shielding from various gases such as water vapor or oxygen and for wrapping or packaging edibles, industrial articles and medicines for preventing them from being deteriorated. Apart from its applications for wrapping and packaging articles, in addition, the gas-barrier film is being used in liquid-crystal display devices, solar cells and EL devices.
In recent development of image display devices such as liquid-crystal display devices and EL devices, the transparent substrate to constitute these devices is required to be lightweight and has a large panel size and, in addition, it is further required to satisfy high-level requirements in that it has long-term reliability and has a lot of latitude in designing its shape and that it enables curved-face display. For the transparent substrate capable of satisfying such high-level requirements, a plastic substrate is being used as a new type of substrate substitutable for a conventional glass substrate that is heavy and readily cracked or broken and hardly worked into a large-size panel. Not only satisfying the above requirements, but also the plastic substrate is applicable to a roll-to-roll system, and therefore it is more advantageous than a glass substrate in that the producibility with it is high and the production cost with it is low.
However, the film substrate of transparent plastics or the like is problematic in that its gas-barrier property is inferior to that of a glass substrate. When a substrate having a poor gas-barrier property is used, water vapor and air may penetrate through it; and, for example, when it is used in liquid-crystal display devices, the liquid crystal in the liquid-crystal cell may be degraded and the degraded part may be a display failure, thereby worsening the display quality of the devices. For solving the problem, a gas-barrier laminate film that comprises a thin metal oxide film formed on a substrate film has been developed. For example, as a gas-barrier laminate film for use in wrapping materials and liquid-crystal display devices, there are known a plastic film coated with silicon oxide through vapor deposition (JP-B-53-12953), and a plastic film coated with aluminium oxide through vapor deposition (JP-A-58-217344). These have a water-vapor barrier level of 1 g/m2/day or so.
However, large-panel liquid-crystal display devices and high-definition display devices developed these days require plastic film substrates having a water vapor permeability of at most 0.1 g/m2/day. Further recently, the development of organic EL devices and high-definition color liquid-crystal display devices is being more promoted, and they require transparent plastic film substrates having a transparency level applicable to them and having a further improved barrier capability (especially having a water vapor permeability of at most 0.01 g/m2/day). To satisfy these requirements, some methods expected to produce a higher gas-barrier level have been investigated, for example, a sputtering method of forming a thin film by the use of a plasma generated through glow discharge under low pressure, and a CVD method for film formation. In addition, also proposed is an organic light-emitting device provided with a barrier film having an alternate laminate structure of organic layer/inorganic layer fabricated according to a vacuum evaporation method (U.S. Pat. No. 6,268,695, from page 4 [2-5] to page 5 [4-49]). Further, for giving the necessary folding resistance enough for application to flexible image displays to a plastic film, disclosed is a technique of using a polymer formed through polymerization of an acrylic monomer and having a volume shrinkage of less than 10% as an organic layer of the film (JP-A-2003-53881, from page 3 [0006] to page 4 [0008]).
However, for use for flexible organic EL substrates, they are still unsatisfactory in point of the bas-barrier capability thereof since the adhesion between the organic layer and the inorganic layer therein is insufficient; and therefore it is desired to further improve them.